Many steps have been taken to improve the fuel economy of automobile engines over the years. To obtain maximum economy, an engine must operate at the highest practical combustion temperatures and pressures. These are limited by many factors, such as the octane rating of the fuel to be used, the fuel to air ratios, the engine operating temperatures, and the temperature of the air entering the inlet manifold, and other less important items. These combustion temperatures are now at their practical upper limits during full throttle operation, which operation represents a very small percentage of total operating time for the average driver. Since a large displacement engine is needed for power at low engine rpm and for accelerating, these large engines have been provided in the past. However, to meet present economy requirements, small displacement engines operating at high rpm to deliver the power required are now in use. They often need superchargers and four valves per cylinder to maintain an acceptable torque at high engine rpm. A multispeed transmission is also needed, but all of these improvements are expensive and provide only modest economy gains. Basically, the present engines are at the practical limit in fuel economy.
The obvious answer to the fuel economy problem is to use a variable displacement engine that operates most of the time in a small displacement mode at near peak efficiency, and which quickly shifts to maximum displacement when high power is required.
Engineers have long recognized the need for a variable displacement engine to obtain a substantial gain in fuel economy and the performance demanded by the majority of users.
Equally important is the pollution problem, which a variable displacement engine would reduce in two ways, i.e., by burning less fuel, and burning the fuel that is consumed in a narrow band of high pressure and temperature.
Therefore, many variable displacement and compression ratio engines have been designed. It is believed that the axial cylinder engine is the only practical design that permits easy displacement change during engine operation.
A good summary and discussion of these engines is found in a publication by E. S. Hall, entitled "Engines Having Cylinders Parallel to the Shaft," published by The Round Engine Patents, New York City.
A variable displacement or variable compression ratio engine is shown in U.S. Pat. No. 4,077,269 to Hodgkinson. The mounting of the swash plate of that device permits variation of its angular orientation to the drive shaft to thereby vary the piston stroke and also permits axial movement to control the compression ratio.
Another variable stroke axial cylinder engine is shown in U.S. Pat. No. 4,294,139 to Bex, et. al.
Still another variable stroke, variable compression ratio engine is shown in U.S. Pat. No. 3,319,874 to Walsh, et. al.
A German patent no. 3043251 to Baye also shows a swash plate engine.
U.S. Pat. No. 3,319,874 shows a means of restraining the wobble assembly that keeps the connecting rods from rotating with the shaft. However, that device can not be balanced due to the variation of the length of the restraint arm, which is radially disposed to slide on an axially disposed straight fixed rod.
Thus, the art is well developed, but despite the acknowledged superiority of a variable displacement engine, none are on the road today. This lack of acceptance is attributable to the heretofore proposed designs' inability to meet the displacement change rates desired for automotive use. Specifically, none of the designs heretofore proposed are able to change from the minimum displacement mode to the maximum at a very fast, but controllable rate when full power is required as for rapid acceleration, and conversely are unable to change to the low displacement mode at a smooth controlled rate when little power is needed.
Equally important is accurate balance. Earlier axial cylinder engine designs, if they addressed balance at all, were of doubtful accuracy over the range of displacement changes and were overly complicated in structure and difficult to manufacture. Furthermore, none of the earlier designs appear to be designed for easy production. Thus, high cost would be another factor against acceptance.
There is a great need, therefore, for an improved axial cylinder variable displacement engine. More specifically, the improved engine would be free of all deficiencies mentioned above, i.e., it would be controllable for the rates of change in displacement required, be balanced over the range of displacements, and most importantly it would have an economically feasible design.
However, the prior art when taken as a whole neither teaches nor suggests how such an acceptable engine could be provided.